The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. H11-196794, filed Jul. 9, 1999. The contents of that application are incorporated herein by reference in their entirety.
1. Field of the Invention
This invention relates to the cutting insert for intermittent cutting which is used in milling tools such as face milling cutters, end-mills and others.
2. Description of the Background
FIG. 4 is the front view of a cutting insert as one example of the conventional technology. FIG. 5 is the cross sectional view along the Xxe2x80x94X line of the cutting insert shown in FIG. 4.
FIG. 6 is the central sectional view of a face milling cutter equipped with the cutting insert shown in FIG. 4. As shown in FIG. 4, this cutting insert is formed in the shape of an approximately square shape (FIG. 4 is approximately square shape) board type and has an under surface 11 which makes a taking a seat side, and an upper face 12 which counters the under surface 11. A main cutting tooth 13 is formed in a ridge line portion which extends approximately to the neighborhood of the upper surface 12, an approximately straight line sub cutting tooth 14 is formed between two main cutting teeth 13, 13 by which it is formed, respectively, and the circular corner tooth 15 is formed between the main cutting tooth 13 and the sub cutting tooth 14 , and a circular corner tooth connects both of the cutting teeth 13, 14 smoothly. A side face 16 which is formed between the under surface 11 and the upper surface 12 inclines outside towards a field 12 and forms a positive insert as shown in FIG. 5.
The upper surface 12 is made into a rake face, and the side face 16 is made into a flank face.
Moreover, a central portion of the upper surface 12 and the under surface 11 is penetrated, and the penetrations for screw penetration is formed.
A ridge line portion which makes approximately four rounds of the upper surface 12 is given a honing (honing surface) 18 as shown in FIG. 4 and FIG. 5. That is, an intersection ridge line portion of the honing 18 and the side face 16 make up the main cutting tooth 13, the sub cutting tooth 14 and the corner tooth 15. The section of this honing 18 which intersects perpendicularly with a ridge line portion may be made into a straight line, and it may extend from this honing 18 toward the outside of the cutting insert 10 to a level surface. The inclination angle (honing angle) xcex8 may be set constant.
The upper surface 12 of the cutting insert 10 consists of an upper surface inclination portion 12A which inclined so that a honing 18 may be intersected, it may extend to the level surface towards the central portion of the cutting insert 10 and become a slope, and an upper surface level part 12B which is connected to this upper surface inclination part 12A, and is leveled in near the central portion of the cutting insert 10. In addition, the connection between upper surface inclination part 12A and the upper surface level part 12B is smoothed.
As shown in FIG. 6, This cutting insert 10 is provided in a tip perimeter of a main cutter body 21 in a milling cutter 20, for instance , and a part of work material is intermittently cut off by carrying out rotation cutting of the main cutter body 21 to the work material.
The cutting insert 10 is disposed so that the main cutting tooth 13 may project toward the perimeter side of the main cutter body 21, and also that sub cutting tooth 14 may turn onto a down tooth of the main cutter body 21. In case of rotation cutting of the work material by the face milling cutter 20, main cutting is performed by the main cutting tooth 13, and finish cutting is performed by the sub cutting tooth 14.
Although the main cutting tooth 13 and the sub cutting tooth 14 is connected smoothly by circular corner tooth 15 in above mentioned cutting insert 10, the problem of being easy to break out in corner tooth 15 by the shocks at the time of the instruction to which each cutting tooth 13, 14, 15 begin to hit to the work material at the time of cutting.
Moreover, the corner tooth 15 in a center side of rotation such as face milling cutter and end mill etc., bites the chips generated by cutting of the sub cutting tooth 14, as the results, the finished surface is damaged, moreover, as the results of the crush the chip into above mentioned corner tooth 15, the corner tooth 15 will be broken.
Furthermore, when the vibration of the work material propagate to the corner tooth 15 at the time of cutting, there was also a problem that the corner tooth 15 will be broken.
Also, the corner tooth 15 located toward the center of rotation in face milling cutters, end mills and others bites the chips generated by the sub cutting tooth 14 during cutting. As a result, a finished surface is damaged and the corner tooth 15 is damaged as well because of the chips crushing into it.
Furthermore, when the vibration of a work material during cutting is transmitted to the corner tooth 15, the corner tooth 15 can break.
In view of the above, this invention aims to offer the cutting insert which is possible to increase the break resistant property of the corner portion near the intersection part of the main cutting tooth and the sub cutting tooth for cutting.
To attain the above mentioned object, a cutting insert according to this invention includes a main cutting tooth having a honing angle xcex1; a sub cutting tooth having a honing angle xcex2; and a corner tooth connecting said main cutting tooth and said sub cutting tooth and having a honing angle xcex3, wherein said honing angle xcex1 is larger than said honing angle xcex2 and said honing angle xcex3.
In the cutting insert mentioned above, since the honing angle over a corner edge is enlarged compared with the honing angle over the main cutting tooth and sub cutting tooth, the break resistance of the corner tooth is increased from easily breaking, therefore, the corner tooth is prevented from easily breaking from the shock exerted on when cutting begins. Since a honing angle is enlarged only against the corner tooth, the sharpness of the main cutting tooth and the sub cutting tooth is not reduced.
Furthermore, another cutting insert according to the present invention includes a corner tooth having a height from an under face which makes the seat face of the corner tooth being lower than a height of a sub cutting tooth.
Since the height from the under face of the corner tooth is lower than the height of a sub cutting tooth in the cutting insert mentioned above, a corner tooth is in a lower position than a sub cutting tooth with respect to a rotational direction of a face milling cutter, an end mill or others. Hence, when the chips generated by a sub cutting tooth during cutting drift toward the center of their rotation, the corner tooth is prevented from biting the chips by the side of a rotation center or breaking by the crash of the chips into the corner tooth.
Moreover, because there is a very small clearance between the corner tooth used for cutting and a work material, when the vibration of the work material is transmitted to the corner tooth during cutting, the corner tooth is prevented from breaking.
Furthermore, still another cutting insert according to the present invention includes the honing angle xcex1 in a range of 0xc2x0 less than xcex1 less than 60xc2x0, the honing angle xcex2 in a range of 0xc2x0 less than xcex2 less than 60xc2x0, and the honing angle xcex3 in a range of 5xc2x0 less than xcex3 less than 80xc2x0.
In the above mentioned cutting insert, if the honing angle xcex1 of the main cutting tooth is less than 0xc2x0, the effect of forming the honing face i.e., the break resistant property of the main cutting tooth cannot be increased, and if it is 60xc2x0 or more, the sharpness of the main cutting tooth is reduced.
Similarly, if the honing angle xcex2 of the sub cutting tooth is less than 0xc2x0, the break resistant property of the sub cutting tooth cannot be increased, and if it is 60xc2x0 or more, the sharpness of the sub cutting tooth is reduced. Furthermore, if the honing angle xcex3 of the corner tooth is less than 5xc2x0, the break resistant property of a corner tooth cannot be increased, and if it is 80xc2x0 or more, the sharpness of a corner tooth is reduced.